Advances in plasma processing have provided for growth in the semiconductor industry. Substrate may be processed in a series of operations in which materials are deposited and selectively removed (etching) in order to form trenches, vias, and other features thereon. Consider the situation wherein, for example, a silicon substrate having an insulator layer and a silicon layer is being etched using fluorinated gases such as SF6, NF3, and CF4. A trench may be formed during a vertical etch into a silicon layer. Etching stops when an insulator layer is reached. One skilled in the art is aware that fluorinated gases are less effective etchants of insulator layers, which may be a dielectric formed from organic and/or inorganic materials. Thus, when an etchant reaches the insulator layer, lateral etching may occur on either side of a trench sidewall.
To facilitate discussion, FIG. 1 shows an example of a silicon substrate with notches. A substrate 100 may include a silicon base layer 102. An insulator layer 104 is disposed below a silicon layer 106 which may be disposed below a hard mask layer 108. To etch silicon layer 106, a fluorinated gas may be used to form a trench 110. When insulator layer 104 is reached, fluorinated gases may begin etching away at sidewalls 112 and 114 of trench 110 to create notches (116 and 118).
Notching, or undercutting into silicon layer 106, is undesirable because it may cause unreliability or yield loss in a final product such as a micro electromechanical system (MEMS) device. In some examples, if notches undercut too much of the silicon layer, other device features may be compromised. In an example, notches 120 and 122 have joined together to create a breakthrough 124 which may result in a defective device.
Notching may occur in both high and low frequency plasma processing systems. In a high frequency system, lateral etching component may be more difficult to control, which may result in more notching. Consequently, some manufacturing companies have sacrificed benefits, such as faster etching of a high frequency plasma system, by reverting back to low frequency plasma systems in order to gain control of the lateral etching component.
Since silicon semiconductor industry is a highly competitive market, manufacturing companies are seeking more viable solutions for resolving the notching issues.